As shown in FIG. 4, there is a well known laminating method in which a metal sheet 101, heated in an oven, is then made to contact thermoplastic resin films 102, and the metal sheet 101 and resin films 102 are both pressed by a couple of laminating rolls (nip rolls) 103 and 104 while the film 102 is partially melted by the heat of metal sheet 101 to adhere to metal sheet 101 (see Laid-Open Japanese Patent Hei 4-201237, for example). In such a laminating method, the thickness of the melted portion of film 102 (thickness of a melted layer), and the adhering strength of film 102 to the metal sheet 101 can be controlled to some extent by selecting conditions such as heating temperature of metal sheet 101, distance from the oven to laminating rolls 103 and 104, traveling speed of metal sheet 101, and melting temperature of film 102.
In the conventional method mentioned above, as shown in FIG. 5, for example, in the case of laminating an oriented resin film when film 102 is pressed to the metal sheet 101 by laminating rolls 103 and 104 (see FIG. 4), the high temperature of the metal sheet 101 is transferred to the laminating roll 103 of a low temperature through film 102. While the high temperature causes the film 102 to form a melted layer 105, the pressed metal sheet 101 and film 102 adhere to each other. After passing through the nip between laminating rolls 103 and 104, metal sheet 101 is free from pressure, and the film surface is not further cooled, and then the temperature from the metal sheet is transferred to the whole film, which controls the orientation of oriented layer 106 of the film. Therefore, as the traveling speed of metal sheet 101 and film 102 increase, the temperature of the metal sheet should be lowered in order to control the orientation of the oriented layer because the cooling effect by the laminating rolls is not sufficient. For this reason, it is difficult to perform high speed lamination by the conventional laminating method.
On the other hand, as a method to increase the melted layer by high speed lamination, heating metal sheet 101 to a higher temperature may be applied. But in this case, cooling by the laminating rolls does not fully effect cooling of the film 102 so that the melted layer 105 may be formed throughout the whole film thickness, thus reducing the strength of the film. In addition, in a case where the laminate forms a food can and such wholly melted film is located inside of the formed can, and when content is packed and storaged in it, the film is easily cracked by outer impact, which often causes the packed contents to become spoiled.
It is the first object of the present invention to solve the problem in the conventional method and to provide a manufacturing method for a laminated sheet in which the laminated sheet has its adhesion increased, and the sufficiently increased adhesion can be obtained even by high speed lamination. The second object of the present invention is to provide a manufacturing apparatus for such a manufacturing method.